Samsung Galaxy S4 mini — help with 3g activating in handbag!

I have just swapped my old s2 for an s4 mini. It seems to have a new feature where 3g will activate if you long press the right hand key. Even when locked. This is driving me mad as it activates in my handbag and it will cause me to go over my data allowance. Anyone know if it can be deactivated?